These studies are divided into several areas of investigation. The first area is the phenomenon of compensatory hypertrophy of a remaining kidney following unilateral nephrectomy. Our data suggest this hypertrophy is stimulated, at least in part, by retention of renal-growth-stimulating factors, or renotrophic factors that are excreted in the urine. These studies are designed to characterize the composition and mechanisms of action of these factors, and to examine their effects on renal function. The second area concerns the control of sodium and potassium excretion by the kidney. We have previously reported evidence for potent natriuretic and kaliuretic factors in urine. The proposed studies will examine the effects of these factors on epithelial ion transport, renal hemodynamics, and glomerular ultrafiltration, as well as their compositional nature. A third area concerns the changes in renal hemodynamics that follow urinary tract obstruction. In particular, we will investigate the renal vasoconstriction and decrease in glomerular filtration observed in obstructive nephropathy and examine the role of intrarenal hormonal systems in their pathogenesis.